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---
title: "FAQ"
---
### General
#### What _is_ x402 in a single sentence?
x402 is an open‑source protocol that turns the dormant HTTP `402 Payment Required` status code into a fully‑featured, on‑chain payment layer for APIs, websites, and autonomous agents.
**Is x402 a CDP Product?**
_No._ While Coinbase Developer Platform provides tooling and are the creators of the standard, it is an open protocol (Apache-2.0 license) and you don't need any Coinbase products to use it. We look forward to further clarifying this distinction and making x402 a credibly neutral payment standard.
#### Why not use traditional payment rails or API keys?
Traditional rails require credit‑card networks, user accounts, and multi‑step UI flows.\
x402 removes those dependencies, enabling programmatic, HTTP-native payments (perfect for AI agents) while dropping fees to near‑zero and settling in \~1 second.
#### Is x402 only for crypto‑native projects?
No. Any web API or content provider—crypto or web2—can integrate x402 if it wants a lower‑cost, friction‑free payment path for small or usage‑based transactions.
### Language & Framework Support
#### What languages and frameworks are supported?
Typescript, Python, and Go are reference implementations, but x402 is an **open protocol**.
Nothing prevents you from implementing the spec in Rust, Java, or other languages. If you're interested in building support for your favorite language, please [open an issue](https://github.com/coinbase/x402/issues) and let us know, we'd be happy to help!
### Facilitators
#### Who runs facilitators today?
Multiple organizations operate production facilitators. The protocol is **permissionless**—anyone can run a facilitator. See the [x402 Ecosystem](https://www.x402.org/ecosystem?category=facilitators) for available options, including:
* Community‑run facilitators for various networks and assets
* Private facilitators for enterprises that need custom KYT / KYC flows.
#### What stops a malicious facilitator from stealing funds or lying about settlement?
Every `x402PaymentPayload` is **signed by the buyer** and settles **directly on‑chain**.\
A facilitator that tampers with the transaction will fail signature checks.
### Pricing & Schemes
#### How should I price my endpoint?
There is no single answer, but common patterns are:
* **Flat per‑call** (e.g., `$0.001` per request)
* **Tiered** (`/basic` vs `/pro` endpoints with different prices)
* **Up‑to** (work in progress): "pay‑up‑to" where the final cost equals usage (tokens, MB, etc.)
#### Can I integrate x402 with a usage / plan manager like Metronome?
Yes. x402 handles the _payment execution_. You can still meter usage, aggregate calls, or issue prepaid credits in Metronome and only charge when limits are exceeded. Example glue code is coming soon.
### Assets, Networks & Fees
#### Which assets and networks are supported today?
| Network | CAIP-2 ID | Asset | Fees\* | Status |
| -------------- | --------- | ----- | -------- | ----------- |
| Base | `eip155:8453` | Any EIP-3009 token | fee-free | **Mainnet** |
| Base Sepolia | `eip155:84532` | Any EIP-3009 token | fee-free | **Testnet** |
| Solana | `solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp` | Any SPL token; Token-2022 (v2 only) | fee-free | **Mainnet** |
| Solana Devnet | `solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1` | Any SPL token; Token-2022 (v2 only) | fee-free | **Testnet** |
\* Gas paid on chain; many facilitators offer **zero** facilitator fees (see [ecosystem](https://www.x402.org/ecosystem?category=facilitators) for details).
_Support for additional chains and assets is on the roadmap and community‑driven._
#### Does x402 support fiat off‑ramps or credit‑card deposits?
Not natively. However, facilitators or third‑party gateways can wrap x402 flows with on‑ and off‑ramps.
### Security
#### Do I have to expose my private key to my backend?
No. The recommended pattern is:
1. **Buyers (clients/agents)** sign locally in their runtime (browser, serverless, agent VM). You can use CDP Wallet API to create a programmatic wallet.
2. **Sellers** never hold the buyer's key; they only verify signatures.
#### How do refunds work?
The current `exact` scheme is a _push payment_—irreversible once executed. Two options:
1. **Business‑logic refunds:** Seller sends a new USDC transfer back to the buyer.
2. **Escrow schemes:** Future spec could add conditional transfers (e.g., HTLCs or hold invoices).
### Usage by AI Agents
#### How does an agent know what to pay?
Agents follow the same flow as humans:
1. Make a request.
2. Parse the `PAYMENT-REQUIRED` header.
3. Choose a suitable requirement and sign a payload via the x402 client SDKs.
4. Retry with the `PAYMENT-SIGNATURE` header.
#### Do agents need wallets?
Yes. Programmatic wallets (e.g., **CDP Wallet API**, **viem**, **ethers‑v6** HD wallets) let agents sign `EIP‑712` payloads without exposing seed phrases.
### Governance & Roadmap
#### Is there a formal spec or whitepaper?
* **Spec:** [GitHub Specification](https://github.com/coinbase/x402/tree/main/specs)
* [**Whitepaper**](https://www.x402.org/x402-whitepaper.pdf)
#### How will x402 evolve?
Tracked in public GitHub issues + community RFCs. Major themes:
* Multi‑asset support
* Additional schemes (`upto`, `stream`, `permit2`)
* Discovery layer for service search & reputation
**Why is x402 hosted in the Coinbase GitHub?**
We acknowledge that the repo is primarily under Coinbase ownership today. This is primarily to leverage our best-in-house security and auditing team to ensure the spec is safe and nobody accidentally creates legally ambiguous payment flows. We intend to eventually transfer ownership of the repo to a steering group or open-source committee.
### Troubleshooting
#### I keep getting `402 Payment Required`, even after attaching `PAYMENT-SIGNATURE`. Why?
1. Signature is invalid (wrong chain ID or payload fields).
2. Payment amount is less than the required `amount` in the payment requirements.
3. Address has insufficient USDC or was flagged by KYT.\
Check the `error` field in the server's JSON response for details.
#### My test works on Base Sepolia but fails on Base mainnet—what changed?
* Ensure you set `network: "eip155:8453"` (Base mainnet) instead of `"eip155:84532"` (Base Sepolia).
* Confirm your wallet has _mainnet_ USDC.
* Gas fees are higher on mainnet; fund the wallet with a small amount of ETH for gas.
### Still have questions?
• Reach out in the [Discord channel](https://discord.gg/invite/cdp)\
• Open a GitHub Discussion or Issue in the [x402 repo](https://github.com/coinbase/x402)
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